When components of tea, such as black tea, green tea and oolong tea, are to be extracted, the tea bag system has often been used in a simple method. Generally, paper is often used as a tea bag material for a tea bag. However, because the paper has a dense structure, the paper used as a tea bag material includes the following problems: although the powder leakage is decreased, the paper shows poor transparency and tea leaves in a tea bag are hardly seen; and the paper cannot be heat sealed.
Furthermore, a nonwoven fabric of thermoplastic synthetic fiber has recently been used as a tea bag material. The nonwoven fabric is prepared by compositing a filaments yarn nonwoven fabric and an extremely thin yarn nonwoven fabric, and the powder leakage is decreased by utilizing a filtering effect of the extremely thin yarn. Such a conventional nonwoven fabric of thermoplastic synthetic fiber is excellent in that it can be heat sealed, and that the powder leakage is decreased. However, the nonwoven fabric has the problem that tea leaves in a tea bag cannot be seen due to insufficient transparency, and the like problem. In particular, when tea leaves of a high grade are used, that the state of tea leaves in a tea bag cannot be seen is a great disadvantage.
In order to improve the transparency of a tea bag and the high-grade feeling it gives, a coarse plain gauze fabric is processed to form a bag shape. However, the resultant tea bag allows much powder leakage. Moreover, the tea bag has a problem regarding in waste treatment.
Japanese Unexamined Patent Publication (Kokai) No. 2001-131826 describes biodegradable monofilaments for tea bags composed of a poly(L-lactic acid), having a size of 15 to 35 dtex, and showing a boil-off shrinkage of 20% or less. However, the invention relates to a tea bag prepared from a plain gauze fabric in which monofilaments are used. The tea bag therefore has the problem that it allows much powder leakage when the transparency of the fabric is increased.
Japanese Unexamined Patent Publication (Kokai) No. 2002-105829 describes a method of making a nonwoven fabric, of a thermoplastic aliphatic polyester filament yarn, flexible by subjecting the fabric to bending treatment. The patent publication discloses a filament yarn nonwoven fabric having a fabric weight of 15 to 200 g/m2, a size of 1.0 to 12 dtex and 4 to 50% of a partial heat contact bonded portion. Moreover, the fabric has no problem about refuse in waste treatment because the fabric is biodegradable. However, there is no description in the patent publication of a nonwoven fabric or a tea bag excellent in transparency, powder leakage, and the like.
Japanese Unexamined Patent Publication (Kokai) No. 9-142485 describes a short fiber nonwoven fabric in which cellulose fiber and biodegradable aliphatic polyester fiber are mixed. The nonwoven fabric contains short fiber that has a size of 1 to 10 denier, is partially heat bonded with a ratio of 5 to 50% or entirely heat bonded, has excellent strength and processability, and is easily degraded by microorganisms. The nonwoven fabric is utilized for a bag for raw refuse, etc. However, there is no description in the patent publication of a nonwoven fabric or a tea bag excellent in transparency, powder leakage, and the like.
Japanese Unexamined Patent Publication (Kokai) No. 7-189136 discloses a light-shielding nonwoven fabric for which a sheath-core yarn is used. A sheath-core conjugate yarn formed out of a polymer as a sheath component that contains a decreased amount of inorganic particles, and a polymer as a core component that contains an increased amount of inorganic particles is used for the nonwoven fabric. Because the nonwoven fabric contains a relatively large amount of inorganic particles in the core component, the nonwoven fabric has excellent shielding properties, and is useful for a printing substrate. However, there is no description in the patent publication of a nonwoven fabric or a tea bag excellent in transparency, powder leakage, and the like.
Although Patent Publication WO 02/48443 discloses a nonwoven fabric material for tea bags that is improved in transparency, there is no description about powder leakage.